Digital video that is transmitted through a network, such as the Internet or a cable television system is generally compressed. Compression is desirable because of the limited bandwidth of most transmission channels (e.g. cable, DSL, cellular etc.). In general, spatial compression algorithms include at least three steps for encoding: transform coding, quantization, and entropy encoding.
In a compressed digital video environment, such as those that transmit and display MPEG encoded video content, still images may be presented to an end user, wherein the still images are repeatedly displayed as video. In a cable television environment wherein all information is transmitted as an MPEG video stream, the presentation of still images may be useful when a selection screen or a static webpage is provided to a cable television subscriber.
It is known in the prior art to have scrolling content such as a ticker for display of stock quotes at the bottom of a static image. The image onto which the ticker is placed will be referred to herein as the base image. In order to create a ticker in an encoded video environment, the base image must first be decoded to the spatial domain and then repeatedly re-encoded with the ticker at different positions. In other words, for each frame of video, the static image is re-encoded with the ticker repositioned, so that upon playback the ticker appears to move across the screen.
The decoding of the encoded image data requires substantial processing power, especially when transform decoding of the image. Because of the processing demands in decoding and re-encoding the image data, tickers and other translating data are not provided in a real-time encoded video environment wherein there are many subscribers. In addition to being processor intensive, the decoding and re-encoding of video content degrades the final image that is presented to the subscriber.